Wastewater can be a valuable resource in cities and towns where population is growing and water supplies are limited. In addition to easing the strain on limited fresh water supplies, the reuse of wastewater can improve the quality of streams and lakes by reducing the effluent discharges they receive. Wastewater may be reclaimed and reused for crop and landscape irrigation, groundwater recharge, or recreational purposes.
The provision of water suitable for drinking is another essential of life. The quality of naturally available water varies from location-to-location, and frequently it is necessary to remove microorganisms, such as bacteria, fungi, spores and other organisms like crypto sporidium; salts, heavy metal ions, organics and combinations of such contaminants.
Over the past several years, numerous primary, secondary and tertiary processes have been employed for the decontamination of industrial wastewater, the purification of ground water and treatment of municipal water supplies rendering them safer for drinking. They include principally combinations of mechanical and biological processes, like comminution, sedimentation, sludge digestion, activated sludge filtration, biological oxidation, nitrification, and so on. Physical and chemical processes have also been widely used, such as flocculation and coagulation with chemical additives, precipitation, filtration, treatment with chlorine, ozone, Fenton's reagent, reverse osmosis, UV sterilization, to name but a few.
Numerous electrochemical technologies have also been proposed for the decontamination of industrial wastewater and ground water, including treatment of municipal water supplies for consumption. While growing in popularity, the role of electrochemistry in water and effluent treatment heretofore has been relatively small compared to some of the mechanical, biological and chemical processes previously mentioned. In some instances, alternative technologies were found to be more economic in terms of initial capital costs, and in the consumption of energy. Too often, earlier electrochemical methods were not cost competitive, both in initial capital costs and operating costs with more traditional methods like chlorination, ozonation, coagulation, and the like.
Earlier electrochemical processes required the introduction of supporting electrolytes as conductivity modifiers which adds to operating costs, and can create further problems with the disposal of by-products. Electrochemical processes in some instances have been ineffective in treating solutions by reducing concentrations of contaminants to levels permitted under government regulations. Heretofore, such electrochemical processes have often lacked sufficient reliability for consistently achieving substantially complete mineralization of organic contaminants, as well as the ability to remove sufficient color from industrial waste waters in compliance with government regulations.
Notwithstanding the foregoing shortcomings associated with earlier electrochemical technologies, electrochemistry is still viewed quite favorably as a primary technology in the decontamination of aqueous solutions. Accordingly, there is a need for more efficient and safer electrochemical cell configurations and processes for more economic treatment of large volumes of industrial waste waters, effluent streams and contaminated ground water, including the decontamination of municipal water supplies making them suitable for drinking. Such electrochemical cell configurations should also be useful in the electrosynthesis of chemical products.